Braunite

Braunite is a silicate mineral containing both di- and tri-valent manganese with the chemical formula: Mn2+Mn3+6[O8|SiO4].[2] Common impurities include iron, calcium, boron, barium, titanium, aluminium, and magnesium.

Braunite
Braunite, from San Marcel, Piemonte , Italy
General
CategoryNesosilicates
Formula
(repeating unit)		Mn2+Mn3+6[O8|SiO4]
Strunz classification9.AG.05
Dana classification7.5.1.3
Crystal systemTetragonal
Crystal classDitetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
Space groupI41/acd
Identification
Colorbrownish black, steel-grey
Cleavage{112} perfect
Mohs scale hardness6-​6 1⁄2
Lustersub-metallic
Streakblack
Diaphaneityopaque
Specific gravity4.72 - 4.83
References[1]

Braunite forms grey/black tetragonal crystals and has a Mohs hardness of 6 - 6.5.

It was named after the Wilhelm von Braun (1790–1872) of Gotha, Thuringia, Germany.[2]

A calcium iron bearing variant, named braunite II (formula: Ca(Mn3+,Fe3+)14SiO24), was discovered and described in 1967 from Kalahari, Cape Province, South Africa.[3][4]

References
  1. Mineralienatlas
  2. Mindat
  3. JoHan P. R. De Viliers, The crystal structure of braunite II and its relation to bixbyite and braunite, American Mineralogist, Volume 65, pages 756-765, 1980
  4. Mindat, Braunite-II
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